PaletteSwitcher/wasm.go

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2021-11-21 19:12:16 +00:00
package main
import (
"bytes"
b64 "encoding/base64"
"encoding/hex"
"image"
"image/color"
_ "image/jpeg"
"image/png"
"log"
"syscall/js"
"time"
"github.com/makeworld-the-better-one/dither/v2"
)
var nordPalette, _ = buildPalette([]string{
"2e3440",
"3b4252",
"434c5e",
"4c566a",
"d8dee9",
"e5e9f0",
"eceff4",
"8fbcbb",
"88c0d0",
"81a1c1",
"5e81ac",
"bf616a",
"d08770",
"ebcb8b",
"a3be8c",
"b48ead",
})
func buildPalette(pal []string) (color.Palette, error) {
var palette = make(color.Palette, len(pal))
for i, s := range pal {
b, err := hex.DecodeString(s)
if err != nil {
return nil, err
}
palette[i] = color.RGBA{b[0], b[1], b[2], 0xff}
}
return palette, nil
}
func ditherImage(img image.Image) image.Image {
// Build ditherer
ditherer := dither.NewDitherer(nordPalette)
ditherer.Matrix = dither.FloydSteinberg
// Dither image in a copy
dst := ditherer.DitherCopy(img)
return dst
}
func decodeImage(imageData []byte) (image.Image, error) {
img, imageType, err := image.Decode(bytes.NewReader(imageData))
if err != nil {
return nil, err
}
log.Printf("Decoded image as %v\n", imageType)
return img, nil
}
// DittherNord returns a Promise that takes a UintArray containing a Jpeg or png image,
// and resolves to a string containing a base64 encoded png image.
func DitherNord() js.Func {
return js.FuncOf(func(this js.Value, args []js.Value) interface{} {
imageBytes := make([]byte, args[0].Length())
js.CopyBytesToGo(imageBytes, args[0])
handler := js.FuncOf(func(this js.Value, args []js.Value) interface{} {
resolve := args[0]
reject := args[1]
go func() {
// Decode image from raw bytes
img, err := decodeImage(imageBytes)
if err != nil {
errorConstructor := js.Global().Get("Error")
errorObject := errorConstructor.New(err.Error())
reject.Invoke(errorObject)
}
// Perform dithering
log.Println("Dithering image...")
t1 := time.Now()
ditheredImage := ditherImage(img)
t2 := time.Now()
log.Printf("Image dithered in %v\n", t2.Sub(t1))
// Encode as PNG
buf := new(bytes.Buffer)
png.Encode(buf, ditheredImage)
// Encode as img src b64 string and resolve
encodedImage := b64.StdEncoding.EncodeToString(buf.Bytes())
resolve.Invoke(js.ValueOf(encodedImage))
}()
return nil
})
promiseConstructor := js.Global().Get("Promise")
return promiseConstructor.New(handler)
})
}